i.mx53qsb and ARM Trustzone Techology

[Stefan Kalkowski]

Hello Joseph,

On 11/17/2014 04:04 AM, Joseph Lee wrote:
> Hi
> 
> From the article in this link
> http://genode.org/documentation/articles/trustzone , I understood that
> the DDR RAM in i.mx53 QSB is partitioned off between normal world and
> secure world. I just want to read a file in the normal world from
> application running in the secure side. Is there any possibility to get
> access to any file in normal world from the secure world? thanks for
> your help in advance.
> 

If you want to access files in the "secure world", you first need some
interface in between, which is not existent right now, at least not for
file access. When designing such an interface, e.g. by adding a special
file system driver in Linux that communicates via hypercalls with the
"secure world", you can of course define a dedicated memory area of the
"normal world" to be used to transfer payload.

Although the DDR RAM is partitioned between both worlds that doesn't
mean the "secure world" can't access memory of the "normal world". It
only means that the memory assigned to the "secure world" can be
accessed exclusively by it, and not by the "normal world".

Nevertheless, caution is advised when using shared memory in between
both worlds, as long as the memory might land in the cache of either of
both worlds. The cache is TrustZone aware, and tags all cache lines to
be secure, or non-secure, thereby effectively partitioning the cache.
So if you use shared memory in between "secure" and "normal world" it
needs to be either marked as uncached, or you need to clean the
corresponding cache-lines after writing data to shared memory
respectively invalidate cache-lines before reading data from shared memory.

I hope this clarifies your question?

Regards
Stefan

> Regards,
> Joseph
> 
> 
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-- 
Stefan Kalkowski
Genode Labs

http://www.genode-labs.com/ · http://genode.org/